Finding Interest Rates & Lump Sum to Double

a. Your parents will retire in 26 years. They currently have $290,000 saved, and they think they will need $1,700,000 at retirement. What annual interest rate must they earn to reach their goal, assuming they don't save any additional funds? Round your answer to two decimal places. ______%

b.If you deposit money today in an account that pays 9% annual interest, how long will it take to double your money? Round your answer to two decimal places. _________ years